I worked in technical support and in Applications Engineering at one of the major modem manufacturers in the 1990s. I can assure you that Plug'n'Play did not address the RTFM issues. Still had hardware level problems like address/IRQ conflicts with PnP. Still had dumb customers trying to force invalid data rates. An interface that (theoretically) juggles 127 nodes without the need for additional assignment of hardware resources is better than an add-in card with DIP switches or jumpers. A device that automatically figures out how fast it can communicate is better than one where I supply that parameter. A device with a standard cable interface is better than one with a physical connector that can be completely non-functional just because the consumer purchased the wrong cable - you could buy 9-pin or 25-pin (or 9-to-25, or 25-to-9) serial cables that were "straight through" or "null modem" (which reversed send and receive, DSR and DTR, RTS and CTS). You could connect serial devices nigh-effortlessly to 25-pin parallel ports. The physical and signals interface catalyzed a revolution in peripheral design and USB served as a proof that hardware vendors could actually get their act together. I don't think you would have seen the success of the PC System Design Guides promulgated by Microsoft in the late 1990s without the example of USB - at least not on the same level. The fundamental problems that USB addressed pale in comparison with "jeez, I have to download a driver."

In fairness to sexconker, Plug 'n' Play worked over serial. Devices would respond to a pre-defined query with a vendor and device ID that were used by the OS to install the correct driver.

You and I remember RS-232 very differently. Is it 8-N-1 or 7-E-1? I have to convince this guy to set his bit rate on COM2 to 19,200 even though the box his modem came in says 14,400 bps in big letters - but I'd have him set it even higher (blazing 115,200) if he didn't have a sluggish 8250 UART. What command set does my modem use? Looks like my dialer doesn't support non-Hayes configuration so I have to download a profile using Zmodem (with my old modem - hope autostart will work today) from a local BBS. Failing that, I will have to decrypt the handy command set reference at the back of the manual. But wait, is the serial port sharing an IRQ level with another peripheral that will cause the connection to seize or the OS to lock up? Looks like I'll have to check the BIOS settings and the jumper settings on the add-in ISA cards that are already installed. Remind me again how little has changed?